It is generally desirable for utility companies to collect meter reading information from homes or commercial establishments without visually inspecting every meter at its resident location. The traditional labor intensive collection system is too expensive to be maintained and the accuracy of the data collected is subject to considerable error. A number of proposals for remote meter reading have been made and some have been put into operation. One system which has been tried uses a radio link with the meter and a mobile radio unit which is driven around selected neighborhoods to collect data from local meters. This requires manned operation of the mobile units and thus is a compromise which uses less labor than the traditional data collection method. Still another system for remote meter reading uses telephone communication between the utility company and the meters to be read. The present invention pertains to this category.
Telephonic meter reading systems have long been proposed without commercial success although in recent times there has been a renewal of commercial attempts which seek to capitalize on improving telephone communication technology. In general, these systems incorporate a modem in each residential unit to receive interrogation signals from the telephone line and to formulate and transmit meter readings via the telephone line to the utility company. Such modems have come into widespread use for telephone communication and are characterized by two traits: they are expensive and unreliable as communication devices. Even though a modem might accurately produce signals representing the data to be transmitted, the signals are in such a form that, due to noise interference or limited system fidelity, they are not faithfully transmitted over normal telephone lines. Some systems use communication devices which may not be recognized as modems, yet the transmission reliability is questionable. Some representative patented systems are described below.
The U.S. Pat. No. 3,842,218 to DeLuca et al describes a system for remote meter reading by telephone which uses a modem (FIG. 5) at the meter site for initiating the interrogation of meters upon receiving a command signal and generating a series of tones to communicate the meter consumption information. The meters have decades supplying signals on ten lines to the tone generator which yields data in decimal form.
The U.S. Pat. No. 3,868,640 to Binnie et al discloses a remote meter reading system using telephony. In one version using a frequency division multiplex basis, a unit at the meter site has four tone decoders and an interrogation signal comprising up to four simultaneous frequencies is evaluated by the unit for prompting a response. In another version using a time division multiplex basis, a single tone decoder is used and the interrogation signal comprises a binary code made up of a series of single frequency tones each representing a "1" or "0". In either version the unit responds by transmitting the meter readings in the form of a series of tones of the same frequency.
The U.S. Pat. No. 3,842,206 to Barselotti et al shows a remote meter reading system having a meter unit which transmits meter readings as a serial binary pulse train. Each bit in the pulse train comprises either of two frequencies representing a "1" or "0".
The U.S. Pat. No. Re. 26,331 to Brothman et al discloses a remote meter reading system having a unit at the meter site for transmitting a coded meter reading in the form of a modulated AC signal in one version or in the form of serial binary pulses interspersed with synchronization pulses in another version.
U.S. Pat. No. 4,587,536 to Oliver et al granted Mar. 25, 1986, discloses a meter reading system including interface means between the meter and telephone line for sending AC signals to the central office in response to an interrogation signal. Plural multiplexers are provided at the central office for multiplexing the signals between a group of telephone lines and central office. A computer selects a multiplexer and one of the telephone lines and a continuous DC and AC coupling is established to the telephone line during on-hook conditions. The interface means generates DTMF signals corresponding to the meter reading value which are transmitted over the telephone line to the central office.
The Lumsden U.S. Pat. No. 4,388,690 granted June 14, 1983, discloses an automatic meter reading transponder. The transponder includes a CPU connected to a receiver and transmitter and a real time clock is connected to the CPU. The CPU receives the input pulses representative of electric power consumption. The RAM of the CPU has a plurality of addressable registers wherein the CPU equates each register sequentially with a predetermined time period. Each register contains a count which is representative of the power consumed during the associated time period.